A chromatograph/mass spectrometer is an apparatus for creating a chromatogram of a sample. It includes a chromatograph unit (e.g. a gas chromatograph or a liquid chromatograph) for separating the sample into components in the order of time, and a mass spectrometer unit for detecting one or more components each having a specified mass number (i.e. mass-to-charge ratio). The chromatogram may be converted into an analogue or digital signal and supplied to a fraction collector which separately collects each component (for example, see paragraphs 0002 to 0005 and FIG. 4 of the Japanese Unexamined Patent Publication No. 2004-198123) or a similar device. Any device that uses chromatogram signals has one or more parameters relating to the use of the supplied signal for specific operations, so that these parameters should be correctly determined for the signal to be properly used.
There are many types of mass spectrometers that are capable of simultaneously observing plural chromatograms under different conditions. For example, they may be chromatograms of plural kinds of ions monitored under an SIM (Selected Ion Monitoring) measurement, or plural mass chromatograms obtained through a scanning measurement. To send plural chromatograms simultaneously obtained under different conditions to another apparatus requires a special technique if there is only one analogue or digital output port available. For example, some conventional chromatograph/mass spectrometers add or average the plural signals to produce a single composite signal.
The composite signal produced through the adding operation is accompanied by the following problems: In general, each chromatogram peak corresponding to each component of the sample appears on only one or a few chromatograms before the adding operation, as shown in FIG. 3, of the instant application. Therefore, the peak intensity never changes even if the number of the signals added is increased. However, the baseline, which corresponds to the noise contained in the signal, becomes higher because the adding operation multiplies the level of the baseline by the number of the signals added together. If there is a peak having a large intensity as in the first chromatogram in FIG. 3, the adding operation may make the peak signal saturated as shown by the circle P, which results in the resultant composite signal having an incorrect waveform.
In contrast, the averaging operation doesn't significantly change the level of the baseline, as shown in FIG. 4, of the instant application. However, this operation divides the intensity of the chromatogram peak by the number of the signals used, thereby making the peak shorter.
To avoid these problems, the operator of the conventional mass spectrometer needs to take the trouble to appropriately change the parameter setting of the fraction collector or other apparatuses that use chromatogram signals whenever the number of the signals used is changed. Taking this problem into account, the present invention intends to provide a new chromatograph/mass spectrometer, which neither raises the level of the baseline nor reduces the height of the chromatograph peak through the composition process, and in which a change in the condition or the number of the signals to be used in the composition process doesn't require the operator to change the parameter setting of apparatuses that use chromatogram signals produced by the mass spectrometer.